Existing night vision systems have many applications in everyday life. Perhaps the most well known use for night vision systems is by the military when performing nighttime maneuvers. The night vision systems permit vision under very low light conditions by converting incoming infrared and/or visible light from a viewed scene to an intensified visible light image. During nighttime maneuvers, military personnel are often performing other tasks, such as piloting an aircraft or driving a vehicle, that require the freedom of their hands while they visually scan the territory. Accordingly, night vision systems have been developed to be worn upon the head of a user, such as goggles being secured directly on the head or by being mounted to a helmet or a visor.
Placing a night vision system on the head of a user places significant constraints upon the optical design of the system. For example, goggles worn upon the head of a user must be both compact and light in weight because excessive weight or excessive front-to-back length of the goggles can cause the goggles to exert large moments on the user's head, causing severe instability problems and preventing their effective use in applications in which the user's head may be subjected to high gravitational or centrifugal loads. Furthermore, in a wide field-of-view optical system, the focal length of the eyepiece optics must be shortened correlatively with that of the wide angle objective for unity magnification. In night vision goggles, this results in insufficient eye relief between the eyepiece optics and the eye, which not only causes discomfort to the user, but also interferes with the ability to position a helmet visor, eyeglasses, and other structures between the goggles and the eyes of the user. In order to compensate for inadequate eye relief, prior night vision goggles have generally been limited to providing a field of view of no more than about 40 degrees.
Night vision goggles have been used in military aviation for several years with fields of view ranging from 30 degrees (Early Cat's Eyes night vision goggles from GEC-Marconi Avionics) to 45 degrees (NITE-OP and NITE-Bird night vision goggles, also from GEC-Marconi Avionics). The vast majority of night vision goggles used in military aviation have a 40-degree circular field of view (AN/AVS-6 and AN/AVS-9). A major limitation of such prior art devices is that increased field of view could only be obtained at the expense of resolution since each ocular uses only a single image intensifier tube and each image intensifier tube has a fixed number of pixels. Therefore, if the fixed numbers of pixels is spread over a larger field of view, then the angular subtense per pixel increases, which translates into reduced resolution. Understandably, increased field of view is a major enhancement desired by military aviators, closely followed by resolution. In conventional goggles, both eyes also typically see the same field of view, i.e., there is a 100-percent overlap of the image viewed by both eyes of the observer. Such a limited field of view greatly restricts the effectiveness of the night vision apparatus.
Night vision systems enjoying an enlarged or panoramic field of view of up to 60 degrees or more and having improved visual acuity have been developed to address this issue. Such systems include additional optical channels mounted adjacent the existing binocular channels to expand the field of view without sacrificing resolution. However, such systems are expensive and must necessarily obviate existing binocular systems when the user upgrades. Moreover, to upgrade from binocular to panoramic capabilities, the old binocular systems must be discarded and replaced by new panoramic systems. For many users, even those enjoying large military budgets, a large-scale upgrade thus represents a significant expense.
Further, as it is often the case that only a few individuals need panoramic night vision at any given time (and it is not always the same few), it is attractive to be able to purchase and use the less expensive binocular systems for the average user and stock only enough of the more expensive panoramic systems as is necessary. While it is not inconceivable to swap out panoramic night vision systems, such systems are often helmet mounted, with the helmets being customized to comfortably fit a single wearer. In addition, failure of any one of the panoramic channels means that the entire unit will be out of service while it is either repaired or replaced. Furthermore, the unitary design of some night vision goggles results in removal of one module affecting the performance (mechanically, optically, and/or electrically) of the remaining module(s).
In some existing night vision systems, a heads-up display may be shown in the field of view of the user by adding the HUD graphics to the output of one of the image intensifier channels. The channel through which the HUD is output, however, is not selectable to match the dominant eye of the user. In other systems, where the night vision goggles are fitted with a HUD and a camera for recording the scenery being viewed, the systems are unable to record both the scenery being viewed and the HUD content so that the recording matches substantially exactly what the user is being shown through the eyepiece.
Furthermore, many night vision systems fail to provide components that are modular in optical, mechanical, and electrical terms, so that removal of one component essentially disables the system mechanically, optically, and electrically. Many existing designs fail to take into account that most individuals have a dominant eye and a weaker eye, the systems having only a predetermined side on which the heads-up display can be shown. Still further, existing systems do not record both the heads-up display content and scenery when a camera/recorder is implemented.
Thus, a need still remains for a night vision system that is readily upgradeable from binocular to panoramic field of view, wherein the panoramic capability may be readily transferred from binocular unit to binocular unit, and wherein the failure of any given optical module does not require the entire unit to be out of service for any appreciable length of time. Various forms of the present invention address these needs, among others.